TTX-sensitive Na+ and nifedipine-sensitive Ca2+ channels in rat vas deferens smooth muscle cells

Abstract

The inward currents in single smooth muscle cells (SMC) isolated from epididymal part of rat vas deferens have been studied using whole-cell patch-clamp method. Depolarising steps from holding potential -90 mV evoked inward current with fast and slow components. The component with slow activation possessed voltage-dependent and pharmacological properties characteristic for Ca(2+) current carried through L-type calcium channels (I(Ca)). The fast component of inward current was activated at around -40 mV, reached its peak at 0 mV, and disappeared upon removal of Na ions from bath solution. This current was blocked in dose-dependent manner by tetrodotoxin (TTX) with an apparent dissociation constant of 6.7 nM. On the basis of voltage-dependent characteristics, TTX sensitivity of fast component of inward current and its disappearance in Na-free solution it is suggested that this current is TTX-sensitive depolarisation activated sodium current (I(Na)). Cell dialysis with a pipette solution containing no macroergic compounds resulted in significant inhibition of I(Ca) (depression of peak I(Ca) by about 81% was observed by 13 min of dialysis), while I(Na) remained unaffected during 50 min of dialysis. These data draw first evidence for the existence of TTX-sensitive Na(+) current in single SMC isolated from rat vas deferens. These Na(+) channels do not appear to be regulated by a phosphorylation process under resting conditions.

Characterization of a voltage-dependent Na+current in human esophageal smooth muscle

“…The TTX sensitivity of the current (IC 50 ϳ20 nM), combined with its insensitivity to Cd 2ϩ , indicates that cultured HESMCs express channels similar to those found in skeletal muscle and neurons, but not those found in cardiac muscle (2). This finding is consistent with the characteristics of some Na ϩ channels found in the smooth muscle of humans (28,35,38) and animals (6,25,30). In contrast, a recent report of voltage-dependent Na ϩ channels in human jejunal SMCs found them to be relatively resistant to blockade by TTX (20).…”

“…Voltage-dependent Na ϩ currents have been recorded in a number of smooth muscle tissues, including arterial (10), lymphatic (19), uterine (36,37), and vas deferens smooth muscle (6). In the gastrointestinal tract, Na ϩ current has been observed in the ileum (30), large intestine (35), and fundus (25).…”

Voltage-gated potassium currents in rat vas deferens smooth muscle cells

“…We have shown previously that the voltage-gated inward current in smooth muscle cells (SMCs) isolated from the epididymal part of the rat vas deferens is carried not only through the L-type Ca 2+ channels but also through the classical tetrodotoxin (TTX)-sensitive Na + channels [2]. The present study addresses the voltage-gated outward K + currents in these cells.…”

“…To investigate the voltage-gated components of the whole-cell outward K + current 2.5 mM CaCl 2 was replaced with 0.5 mM CdCl 2 and 2 mM MgCl 2 to eliminate the effects of voltage-gated Ca 2+ channels and diminish Ca 2+ -dependent K + current. In addition, PSS also contained 1 M TTX to block voltage-gated Na + current [2].…”

Outward current components in single smooth muscle cells from the ratvas deferens

“…4-Aminopyridine inhibited fast inactivating outward current (Kr) evaluated by digital subtraction in the Ca 2+-free medium in the presence of 1 ~tM tetrodotoxin (TTX), to eliminate inward voltage-gated Na + and Ca 2+ currents [ 1 ]. Inhibition developed in a dose-dependent manner with a half-maximum blocking ICs0 = 0.3 + 0.1 mM (n = 6).…”